Methods of processing semiconductor wafer, and producing IC card, and carrier

ABSTRACT

A semiconductor wafer is made thin without any cracks or warp under good workability. The semiconductor wafer thinning process includes the first step of preparing a carrier formed of a base and a suction pad provided on one surface of the base or formed of a base film with an adhesive, the second step of bonding a semiconductor wafer to the carrier in such a manner that a rear surface of the semiconductor wafer with no circuit elements formed therein is opposite to the carrier to form a wafer composite, and the third step of holding the carrier of the wafer composite with its semiconductor wafer side up and spin-coating an etchant on the rear surface of the semiconductor wafer thereby to make the semiconductor wafer thin.

TECHNICAL FIELD

The present invention relates to semiconductor wafer processingtechniques, and particularly to a technique effective for use inhandling semiconductor wafers when the semiconductor wafers areprocessed to a very small thickness of 100 μm or below.

BACKGROUND ART

In semiconductor devices that we required to be thin as well as of highdensity and small size, such as semiconductor devices applied to ICcards, ever thinner packages, are used, such as TQFP (thin quad flatpackage) and TSOP (thin small outline package). In order to manufacturesuch packages, it is necessary to make the semiconductor wafersparticularly thin. Here, the known techniques for making thesemiconductor wafers thin, as for example described in “PRACTICALLECTURES VLSI PACKAGING TECHNOLOGY (the second volume)” published byNIKKEI BP Co.,Ltd. on May 31, 1993, pp. 12 to 14, are grinding, chemicaletching and lapping. As in the publication, grinding is a technique forgrinding rear surface of a semiconductor wafer with a diamondgrindstone, a etching is the technique for etching the rear surface of asemiconductor wafer with a mixture of chiefly fluoric acid and nitricacid while the semiconductor wafer is being rotated with high speed, andlapping is a technique for grinding the rear surface of a semiconductorwafer with abrasive grains.

The thinning process by the grinding or lapping is able to grindsemiconductor wafers of general thickness, or about 625 μm (or 725 μm)to a thickness of about 300 μm, but has a difficulty when trying togrind to a thickness of, for example, 100 μm or below because thesemiconductor wafer might be cracked even under strict care whenremoving it from the grinder. Even if the wafer is not cracked, it isremarkably warped depending on the stress in the passivation film on thewafer surface and the internal stress of the wafer. This warp causesoperational problems in the following processes such as dicing. Inaddition, it is difficult to process large-diameter semiconductorwafers, or 12-inch or above wafers to a specified level of flatness anduniformity.

Moreover, in the thinning process by etching, since the wafer is rotatedat high speed, an excessive stress is exerted on the semiconductor waferby the pins that hold its outer peripheral portion at a plurality oflocations, thus breaking the wafer. Furthermore, a warp will occur dueto the internal stress as in the grinding.

In order to solve the above problems, the inventors have found to fixthe semiconductor wafer to a certain support base with tape and processit after various examinations. However, normal tape is also discardedafter use in the process of each wafer, thus increasing the cost, orcausing a new problem.

Accordingly, it is an object of the invention to provide a techniquecapable of making semiconductor wafers thin without any crack by solvingthe above technical problems.

It is another object of the invention to provide a technique capable ofmaking semiconductor wafers thin under easy operation.

It is still another object of the invention to provide a techniquecapable of making semiconductor wafers thin without any warp.

It is a further object of the invention to provide a technique capableof making semiconductor wafers thin at low cost.

The features of the invention, and the above objects of the inventiontogether with other objects will be best understood by the followingdescription, taken in conjunction with the accompanying drawings.

DISCLOSURE OF INVENTION

A typical one of the inventions disclosed in this application will bedescribed briefly as below.

The semiconductor wafer processing method according to the inventionincludes a first step of preparing a plate-like or film-shaped carrierthat is formed of a base and an adhesive member provided on one surfaceof the base, a second step of producing a wafer composite by bonding asemiconductor wafer to the carrier in such a manner that the rearsurface of the wafer with no circuit elements formed therein is oppositeto the carrier, and a third step of making the semiconductor wafer thinby spin-coating an etchant on the rear surface of the semiconductorwafer of the wafer composite that is supported with its semiconductorwafer side up.

In this semiconductor wafer processing method, the semiconductor waferof the wafer composite is made to have a larger diameter than thecarrier so that all the outer peripheral edge of the semiconductor waferoverhangs from the carrier when the wafer composite is formed by bondingthe wafer on the carrier. In the third step, the semiconductor wafer canbe thinned while a gas is being blown from below against the wafercomposite. In addition, the semiconductor wafer may be made to have adiameter equal to or smaller than the carrier so that the peripheraledge of the wafer does not overhang from the carrier when the wafercomposite is formed.

Moreover, after the semiconductor wafer is thinned by the third step, afourth step and a fifth step may be provided. The fourth step is forsticking the rear side of the wafer on a dicing sheet and peeling offthe carrier, and the fifth step is for dicing the semiconductor wafer onthe dicing sheet into individual semiconductor chips.

The semiconductor wafer processing method of the invention includes afirst step of preparing a semiconductor wafer with a passivation filmformed on its main surface in which circuit elements are already built,a second step of preparing a plate-like or film-like carrier that isformed of a base and an adhesive member provided on one surface of thebase, a third step of producing a wafer composite by bonding thesemiconductor wafer to the carrier in such a manner that the rearsurface of the wafer with no circuit elements formed therein is oppositeto the carrier, and a fourth step of holding the wafer composite withits semiconductor wafer side up and spin-coating an etchant on the rearsurface of the semiconductor wafer thereby to thin the semiconductorwafer. In this case, after thinning the semiconductor wafer at thefourth step, it is possible to add a fifth step of attaching the rearsurface of the semiconductor onto a dicing sheet and peeling off thecarrier from the wafer composite, and a sixth step of dicing thesemiconductor wafer left on the dicing sheet into individualsemiconductor chips.

The IC card producing method according to the invention includes a firststep of preparing a plate-like or film-like carrier that is formed of abase and an adhesive member provided on one side of the base, a secondstep of producing a wafer composite by bonding a semiconductor wafer tothe carrier in such a manner that the rear surface of the wafer with nocircuit elements formed therein is opposite to the carrier, a third stepof holding the wafer composite with its semiconductor wafer side up andspin-coating an etchant on the rear surface of the semiconductor waferthereby to thin the semiconductor wafer, a fourth step of attaching thethinned rear surface of the semiconductor wafer to a dicing sheet andpeeling off the carrier from the wafer composite, a fifth step of dicingthe semiconductor wafer left on the dicing sheet into individualsemiconductor chips, a sixth step of reducing or loosing or losing theadhesion of the dicing sheet, a seventh step of mounting one or ones ofthe semiconductor chips on a card substrate at chip-mounting positions,and an eighth step of producing an IC card by using the card substratewith the semiconductor chip or chips mounted.

According to the invention, there is provided an IC card producingmethod including a first step of preparing a semiconductor wafer with apassivation film formed on its main surface in which circuit elementsare already built, a second step of preparing a plate-like or film-likecarrier that is formed of a base and an adhesive member provided on onesurface of the base, a third step of producing a wafer composite bybonding a semiconductor wafer to the carrier in such a manner that therear surface of the wafer with no circuit elements formed therein isopposite to the carrier, a fourth step of holding the wafer compositewith its semiconductor wafer side up and spin-coating an etchant on therear surface of the semiconductor wafer thereby to thin thesemiconductor wafer, a fifth step of attaching the thinned rear side ofthe semiconductor wafer to a dicing sheet and peeling off the carrierfrom the wafer composite, a sixth step of dicing the semiconductor waferleft on the dicing sheet into individual semiconductor chips, a seventhstep of reducing or loosing or losing the adhesion of the dicing sheet,an eighth step of mounting one or ones of the semiconductor chips on acard substrate at chip-mounting positions, and a ninth step of producingan IC card by using the card substrate with the semiconductor chip orchips mounted.

When bumps are formed at the chip electrodes of the semiconductor waferin the IC card producing methods of the invention, the thickness of theadhesive member provided on the base should be equal to or larger thanthe height of the bumps. In addition, at the seventh step, it isdesirable to directly mount the semiconductor chips on the cardsubstrate from the dicing sheet.

Moreover, the carrier in the invention is used in the semiconductorwafer processing method, and its adhesive member comprises anelastically flexible suction pad for sucking the semiconductor wafer byvacuum. In this carrier, the suction,pad may have a size large enough tosuck substantially an entire surface of the semiconductor wafer. Inaddition, it may be formed in a ring shape along the outer periphery ofthe semiconductor wafer. Also, a plurality of such suction pads may beprovided over an entire surface of the base in order to hold thesemiconductor wafer at a plurality of locations.

In addition, the carrier in the invention is used in the semiconductorwafer processing method, and its adhesive member comprises a suctiongroove that is formed in the base to be communicated with a vacuum holeconnected to a vacuum pump so that the semiconductor wafer is sucked byvacuum and peeled off from the carrier by restoring to atmosphericpressure.

Also, the carrier in the invention is used in the semiconductor waferprocessing method according to the invention, and its adhesive member isconstituted by a plurality of suction holes which are formed in onesurface of the base at different locations to be communicated with avacuum hole connected to a vacuum pump so that the semiconductor waferis sucked by negative pressure and peeled off from the carrier byrestoring to atmospheric pressure.

Moreover, the carrier in the invention is used in the semiconductorwafer processing method according to the invention, and its adhesivemember comprises a porous member that has a great number of small holesand is provided on one surface of the base for the small holes to becommunicated with a vacuum hole connected to a vacuum pump so that thesemiconductor wafer is sucked by vacuum and that it is peeled off fromthe carrier by restoring to atmospheric pressure.

Also, the carrier in the invention is used in the semiconductor waferprocessing method according to the invention, and its adhesive memberincludes an exfoliation portion coplanar with the base to form aplurality of small recesses, and gelled silicone interposed between thepeeling portion and the semiconductor wafer to make the base adhere tothe semiconductor wafer, whereby when the surroundings of theexfoliation portion are evacuated the silicone is sunk in the recessesso as to be peeled off from the semiconductor wafer. The exfoliationportion of the carrier may be a net or an irregular surface formed onthe base.

In addition, the carrier employed in the semiconductor wafer processingmethod according to the invention has its base made of a transparentmaterial and its adhesive member made of a UV cure-type adhesive ofwhich the adhesion is reduced or lost by ultraviolet rays radiatedthrough the base so that the carrier can be peeled off from thesemiconductor wafer.

Also, the adhesive member employed in the semiconductor wafer processingmethod according to the invention is made of a temperature activationtype adhesive of which the adhesion is reduced or lost by temperaturechange so that the carrier can be peeled off from the semiconductorwafer. The temperature activation type adhesive of this carrier may havesuch a characteristic that its adhesion is reduced or lost at a lowtemperature.

The adhesive member employed in the semiconductor wafer processingmethod according to the invention is a liquid that acts as an adhesivein such a manner that the semiconductor wafer and the base are made inintimate contact with each other by the interfacial force exertedtherebetween and that the semiconductor wafer is peeled off from thebase by ultrasonic waves.

The base of the carrier should be made of an acid-resistant material,for example, compacted fibrous fluororesin.

Thus, since the semiconductor wafer thinning process is performed on thewafer composite formed by bonding the semiconductor wafer to thecarrier, any cracks can be prevented from occurring even with no strictcare when the semiconductor wafer is thinned. In addition, since thereduction of the rigidity of the thinned semiconductor wafer can becompensated for by the carrier so that release of the stress in thepassivation film is prevented, the semiconductor wafer is not warped.Thus, the semiconductor wafer can be stably processed to be extremelythin.

Moreover, since the wafer composite can be handled in the same way asthe semiconductor wafer having a normal thickness before thinning, anycracks can be prevented form occurring on the semiconductor wafer evenwith no strict care, and the work for thinning can be made with ease.

In addition, since the carrier of the wafer composite is supported sothat no unnecessary stress is exerted on the semiconductor wafer, nowarp occurs, and thus the semiconductor can be thinned with highquality.

If the semiconductor wafer is fixed to the base by the suction pad, thecarrier need not be discarded after use and can be simplified in itsconstruction, and thus the semiconductor wafer can be thinned at lowcost.

If the wafer composite is formed by attaching the semiconductor wafer tothe base to overhang from the carrier, and spin-coated with an etchantwhile gas is continuously blown against this wafer composite, theetchant can be surely prevented from flowing around the outer peripheralside into the main surface, whereby the circuit elements are notdamaged.

If the wafer composite is so formed that the outer periphery of thesemiconductor wafer does not overhang from the carrier, the etchant isprevented from flowing around the peripheral side into the main surface,and thus it is not necessary to blow gas against the wafer composite.Moreover, since the thinned semiconductor wafer does not overhang fromthe carrier, the wafer composite can be easy to handle. Also, since theentire main surface of the semiconductor wafer is covered by the carrierso that it is shielded from the external atmosphere, the rear surface ofthe semiconductor wafer can be etched even by dipping.

If an IC card is produced by using semiconductor chips that are producedby dicing the thinned semiconductor wafer, the IC card can be madethinner than the conventional IC card.

If the thickness of the adhesive member provided on the base is madeequal to or larger than the height of the bumps formed on thesemiconductor wafer, the entire carrier is made in intimate contact withthe semiconductor wafer so that both are not peeled off from each other.Also, if the semiconductor chips are directly mounted on the cardsubstrate from the dicing sheet, the additional moving operation for thesemiconductor chips can be omitted, and thus throughput can be improved.

The peeling operation after thinning can be simplified by taking thevacuum suction structure of the carrier for sucking the semiconductorwafer, or by using an adhesive member formed of a peeling portion and anadhesive sheet or formed of UV cure-type adhesive or temperatureactivation adhesive. Moreover, since the semiconductor wafer is alwayskept flat along the base, the warp of the semiconductor wafer can beeffectively suppressed.

Since the carrier formed of an reversible temperature activation typeadhesive can be repeatedly used in the thinning process, the thinnedsemiconductor wafer can be mass-produced at low cost.

Since the carrier having the base made of an acid resistant material canbe repeatedly used in the thinning process, the thinned semiconductorwafer can be mass-produced at low cost.

Since the base may be made of compacted fibrous fluororesin having afeature of resistance against acid, it is possible to use variousdifferent adhesives such as temperature activation type adhesives withweak adhesion to the base.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of the carrier used in the semiconductor waferthinning process of one embodiment of the invention,

FIG. 2 is a cross-sectional view taken along a line II—II in FIG. 1,

FIG. 3 shows part of the semiconductor wafer processing procedure usingthe carrier of FIG. 1,

FIG. 4 is another part of the procedure using the carrier of FIG. 1after the operation of FIG. 3,

FIG. 5 is a schematic diagram of the etching apparatus used in thesemiconductor wafer thinning process according to the invention,

FIG. 6 shows another part of the procedure using the carrier after theoperation of FIG. 4,

FIG. 7 shows another part of the procedure using the carrier after theoperation of FIG. 6,

FIG. 8 shows another part of the procedure using the carrier of FIG. 1after the operation of FIG. 7,

FIG. 9 .shows another part of the procedure using the carrier of FIG. 1after the operation of FIG. 8,

FIG. 10 shows another part of the procedure using the carrier of FIG. 1after the operation of FIG. 9,

FIG. 11 is a plan view of the carrier used in the semiconductor waferthinning process according to another embodiment of the invention,

FIG. 12 is a cross-sectional view taken along a line XII—XII in FIG. 11,

FIG. 13 is a plan view of the carrier used in the semiconductor waferthinning process according to still another embodiment of the invention,

FIG. 14 is a cross-sectional view taken along a line XIV—XIV in FIG. 13,

FIG. 15 is a plan view of the carrier used in the semiconductor waferthinning process according to still another embodiment of the invention,

FIG. 16 is a cross-sectional view taken along a line XVI—XVI in FIG. 15,

FIG. 17 is a plan view of the carrier used in the semiconductor waferthinning process according to still another embodiment of the invention,

FIG. 18 is a cross-sectional view taken along a line XVIII—XVIII in FIG.17,

FIG. 19 is a plan view of the carrier used in the semiconductor waferthinning process according to still another embodiment of the invention,

FIG. 20 is a cross-sectional view taken along a line XX—XX in FIG. 19,

FIG. 21 is a plan view of the carrier used in the semiconductor waferthinning process according to still another embodiment of the invention,

FIG. 22. is a cross-sectional view taken along a line XXII—XXII in FIG.21,

FIG. 23 shows part of the semiconductor wafer processing procedure usingthe carrier of FIG. 21,

FIG. 24 shows another part of the semiconductor wafer processingprocedure using the carrier of FIG. 21 after the operation of FIG. 23,

FIG. 25 shows another part of the semiconductor wafer processingprocedure using the carrier of FIG. 21 after the operation of FIG. 24,

FIG. 26 shows another part of the semiconductor wafer processingprocedure using the carrier of FIG. 21 after the operation of FIG. 25,

FIG. 27 shows another part of the semiconductor wafer processingprocedure using the carrier of FIG. 21 after the operation of FIG. 26,

FIG. 28 shows another part of the semiconductor wafer processingprocedure using the carrier of FIG. 21 after the operation of FIG. 27,

FIG. 29(a) illustrates the state of the bonded semiconductor wafer andcarrier,

FIG. 29(b) illustrates the state of the separated semiconductor waferand carrier,

FIG. 30 shows another part of the semiconductor wafer processingprocedure using the carrier of FIG. 21 after the operation of FIG. 28,

FIG. 31 shows part of the semiconductor wafer processing procedureaccording to still another embodiment of the invention,

FIG. 32 shows another part of the procedure after the operation of FIG.31,

FIG. 33 shows another part of the procedure after the operation of FIG.32,

FIG. 34 shows another part of the procedure after the operation of FIG.33,

FIG. 35 shows another part of the procedure after the operation of FIG.34,

FIG. 36 shows another part of the procedure after the operation of FIG.35,

FIG. 37 shows another part of the procedure after the operation of FIG.36,

FIG. 38 is a plan view of the carrier used in the semiconductor waferthinning process according to still another embodiment of the invention,

FIG. 39 is a cross-sectional view taken along a line XXXIX—XXXIX in FIG.38,

FIG. 40 is a cross-sectional view of the carrier used in thesemiconductor wafer thinning process according to still anotherembodiment of the invention,

FIG. 41 shows part of the semiconductor wafer processing procedureaccording to still another embodiment of the invention,

FIG. 42 shows another part of the procedure following the operation ofFIG. 41,

FIG. 43 shows another part of the procedure following the operation ofFIG. 42,

FIG. 44 shows another part of the procedure following the operation ofFIG. 43,

FIG. 45 shows another part of the procedure following the operation ofFIG. 44,

FIG. 46 shows another part of the procedure following the operation ofFIG. 45,

FIG. 47 shows another part of the procedure following the operation ofFIG. 46,

FIG. 48 shows another part of the procedure following the operation ofFIG. 47,

FIG. 49 shows another part of the procedure following the operation ofFIG. 48,

FIG. 50 shows another part of the procedure following the operation ofFIG. 49,

FIG. 51 shows another part of the procedure following the operation ofFIG. 50,

FIG. 52 shows another part of the procedure following the operation ofFIG. 51,

FIG. 53 shows another part of the procedure following the operation ofFIG. 52,

FIG. 54 shows another part of the procedure following the operation ofFIG. 53,

FIG. 55 is an enlarged plan view of the chip electrode portion of thesemiconductor wafer of FIG. 41,

FIG. 56. is a cross-sectional view taken along a line C₁—C₁,

FIG. 57 shows the details of FIG. 48,

FIG. 58 is a plan view of the internal structure of the IC card producedaccording to this embodiment,

FIG. 59 is a cross-sectional view taken along a line C₂—C₂,

FIG. 60 is an enlarged cross-sectional view of portion A of FIG. 59, and

FIG. 61 is an enlarged cross-sectional view of portion B of FIG. 60.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the invention will be described in detail withreference to the accompanying drawings. In all the figures useful forthe embodiments, like elements are identified by the same referencenumerals, and will not be repeatedly described.

FIG. 1 is a plan view of the carrier used in the semiconductor waferthinning process according to one embodiment of the invention, FIG. 2 isa cross-sectional view taken along the line II—II in FIG. 1, FIG. 3,FIG. 4 and FIGS. 6 to 10 are flow diagrams of the semiconductor waferprocessing procedure using the carrier of FIG. 1, and FIG. 5 is aschematic diagram of the etching apparatus used in the semiconductorwafer thinning process.

The carrier 1 depicted in FIGS. 1 and 2 has a plate-like shape in orderfor the semiconductor wafer 2 (shown in FIG. 3 and other figures) to bestuck and held on the carrier to form the wafer composite 10 (as shownin FIG. 3 and other figures). This carrier 1 is formed of a base 1 a andan elastically flexible suction pad (adhesive member) 1 b provided onone surface of the base 1 a. The base 1 a formed in a disk along theshape of the semiconductor wafer 2 is made of, for example, fluororesin,glass plate or epoxy resin which has resistance to acid. The suction pad1 b to which the semiconductor wafer 2 is stuck is made of, for example,soft rubber having a size large enough to absorb, or adhere tosubstantially one entire surface of the semiconductor wafer 2. In thisembodiment and the following embodiments, the base 1 a constituting thecarrier 1 is preferably made of a material having resistance to acid asdescribed above in order that it can be prevented from changing inquality by an etchant L (FIGS. 5, 6). In addition, in order that thesemiconductor wafer 2 can be prevented from being broken by the actionof concentrated stress by the supporting pins of the etching apparatuson the supported locations of the semiconductor wafer 2 as will bedescribed later, the diameter of the base 1 a is designed to beslightly, for example, about 10 μm larger than the semiconductor wafer2.

The semiconductor wafer 2 stuck on the suction pad 1 b is ground to bethin by the following process.

First, the rear surface of the semiconductor wafer 2, after thecompletion of the pretreatment process up to the electric examinationfor the circuit elements formed on the main surface, is ground to athickness of, for example, about 250 μm with a diamond grindstone orabrasive grains. In this case, immediately the thinning processdescribed later may be performed without this preliminary process.

Then, the semiconductor wafer 2, under the condition that its rearsurface having no circuit elements is directed to the outside, oropposite to the carrier 1, is pressed against the carrier 1 as shown inFIG. 3. When a light weight is loaded uniformly on the entire surface ofthe semiconductor wafer 2, the suction pad 1 b is elastically deformedso that the volume of the pad closed by the wafer 2 is decreased todischarge the internal air. When the load is removed from the wafer 2,the adhesion pad 1 b intends to be restored by itself to the originalshape. As a result, the reduced volume expands somewhat close to theoriginal volume, but air is prevented from flowing into the pad by thewafer 2 that is made in intimate contact with the pad. Consequently, apressure-reduced state is created within the suction pad 1 b, so thatthe wafer 2 adheres by suction to the carrier 1. Thus, the wafercomposite 10 is formed (FIG. 4). While in this embodiment thesemiconductor wafer 2 and carrier 1 constituting the wafer composite 10are equal in their diameters as depicted in FIG. 4, the wafer 2 may havea smaller diameter than the carrier 1 or may have a larger diameter thancarrier as described later.

After the completion of wafer composite 10, a plurality of such wafercomposites with their wafers 2 up are enclosed in a cassette case 20 a(FIG. 5), and carried to the etching process.

FIG. 5 shows the etching apparatus for the wafer composite 10. Theetching apparatus is a spinning-type etcher which coats an etchant L byspinning on the surface of the semiconductor wafer 2. This etchingapparatus includes a loader 30 having the cassette case 20 a, a workingstage 50 on which the wafer composite 10 being processed is placed, andan unloader 40 having a cassette case 20 b in which the processed wafercomposite 10 is enclosed. Also, it has a handler 60 for carrying thewafer composite 10 from the loader 30 to the working stage 50, and fromthe working stage 50 to the unloader 40. The wafer composite 10 iscarried with its rear surface lifted by this handler 50. Because aninert gas such as N₂ gas, or air is blown from below against the wafercomposite placed on the working stage 50, an air spout 70 is providedbeneath the working stage 50. In addition, supporting pins 80 areprovided to grip the wafer composite 10 at, for example, three locations120 degrees spaced along the peripheral edge of the stage 50. Thesupporting pins 80 can be rotated around the working stage 50 by a motornot shown, and thus the wafer composite 10 is rotated around itsrotating axis by the supporting pins 80. A nozzle 90 from which theetchant L is dropped on the semiconductor wafer 2 is further providedabove the working stage 50.

The handler 60 picks up one of the wafer composites 10 from the cassettecase 20 a that has been set in the loader 30 of the etching apparatus,and loads it on the working stage 50 with its wafer 2 side up. Here,since the handler 60 carries the wafer composite 10 with its rearsurface (namely, base 1 a side) lifted, such a shock as to occur whenthe semiconductor wafer 2 side sucked by vacuum is carried is not addedto the semiconductor wafer 2, and particularly the semiconductor wafer 2can be prevented from being cracked after the thinning process.

After loading the semiconductor wafer on the working stage 50, N₂ gas,for instance, is blown from the gas spout 70 against the wafer composite10, to slightly float it from the stage 50, and it is gripped by thesupporting pins 80 when floated. While the N₂ gas is being continuouslyblown against the wafer composite 10, the wafer composite 10 is rotatedat a rate ranging from a few tens of turns to several thousand turns,and the etchant L is dropped from the nozzle on the semiconductor wafer2, thus thinning it as shown in FIG. 6. For assuring the flatness afteretching, it is desired that when the etchant L is dropped, the nozzle 90be moved at a constant speed up to the outer peripheral edge through thecenter of the semiconductor wafer 2 while the distance between thenozzle and the wafer is maintained constant. The etching speed of thedropped etchant L is selected to be, for example, 30 μm/min, and etchingtime is chosen to be, for example, about 400 seconds. In order thatundesired vibration due to the high-speed revolution is prevented fromoccurring, not to wave the etchant L causing uneven etching or not todetach the wafer 2 from the supporting pins 80, the rotation center ismade coincident with the center of the wafer 2. In addition, althoughthe constituents of etchant L to be chosen are dependent on the purposeof etching, it is desired that, in this embodiment for thinning, theetching rate be selected to be as high as 10 μm/min to 100 μm/min.Moreover, when greater importance is attached to the flatness, theetching process may be divided into two steps so that the second etchingstep can be performed with a lower etching rate. While in thisembodiment the etchant L is a mixture of fluoric acid, nitric acid andphosphoric acid, it may be added with a surface active agent forcontrolling the reaction.

In this way, the semiconductor wafer 2 of the wafer composite 10 isetched to be thin up to a thickness of about 50 μm as shown in FIG. 7.In this case, the thickness is not limited to 50 μm, but may bearbitrarily selected. After etching, the semiconductor wafer 2 is rinsedwith pure water, and dried by rotating it at a high speed of 1000 to3000 rpm.

After the thinning process, the wafer composite 10 is unloaded from theworking stage 50 by the handler 60, and carried into the cassette case20 b that is provided in the unloader 40. These processing steps areperformed for each of the wafer composites 10 housed in the cassettecase 20 a of the loader 30. After the processed wafer composites areplaced in the cassette case 20 b, the cassette case 20 b is taken outfrom the etching apparatus.

Then, each wafer composite 10 is drawn out from the cassette case 20 b,and stuck on the dicing tape 4 with a ring 3 attached in such a mannerthat as illustrated in FIG. 8 the rear surface of the wafer 2 can becemented onto the adhesive surface as in the conventional attachment ofwafer 2 on tape. The dicing tape 4 used is formed of, for example, abase made of PET (polyethylene terephthalate), vinyl chloride, polyesteror polyethylene, and an adhesive of acrylic polymer coated on the base.The base and adhesive may be other materials. The dicing tape may be ofthe self-adhesive type in which the base itself has adhesion.

After attaching the wafer composite onto the dicing tape 4, a peelingjig 5 is used to peel off the carrier 1 from the semiconductor wafer 2.Thus, the semiconductor wafer 2 50 μm thick remains stuck to the dicingtape 4 (FIG. 10). Under this condition, the semiconductor wafer 2 can bediced into individual semiconductor chips. After dicing, thesemiconductor chip or chips are mounted on an IC card through, forexample, an anisotropically conductive connection film.

According to the semiconductor wafer processing technique of thisembodiment, since the semiconductor wafer 2 is stuck to the carrier 1 toform the wafer composite 10 which is then handled for the wafer 2 to bethinned, cracks and warps can be prevented without strict care, and thesemiconductor wafer 2 can be stably thinned up to a very small thicknessof, for example, 50 μm.

In addition, since the thinned semiconductor wafer 2 can be handled asif it were a thick semiconductor wafer before thinning, thesemiconductor wafer 2 can be prevented from cracking even without greatcare, and thus it is easy to work for thinning.

Moreover, since the carrier 1 of the wafer composite 10 is held atdifferent locations by the supporting pins 80, the semiconductor wafer 2can be prevented from warping due to the stress by the supporting pins80, and thus it can be thinned with good quality finishing.

Furthermore, since the semiconductor wafer is fixed through the suctionpad 1 b to the base 1 a, waste of tape after use, for instance, can beomitted unlike the case of fixing on tape, and the structure of thecarrier 1 can be simplified, thus permitting the semiconductor wafer 2to be thinned at low cost.

By making the base 1 a of an acid-resistant material, it is possible torepeatedly use the carrier 1, so that the semiconductor wafer 2 can bemass-produced at low cost.

FIG. 11 is a plan view of the carrier in another embodiment of thesemiconductor wafer thinning process according to the invention. FIG. 12is a cross-sectional view taken along the line XII—XII in FIG. 11.

As illustrated, the carrier 1 according to this embodiment has thesuction pad 1 b formed in a ring shape along the outer peripheral edgeof the semiconductor wafer.

According to this carrier 1, since the holding force due to the vacuumof suction pad 1 b is exerted only on the outer periphery of thesemiconductor wafer, not the inner region, it is possible to suppressthe warp in the semiconductor wafer due to the stress on the innersurface region.

FIG. 13 is a plan view of the carrier used in still another embodimentof the semiconductor wafer thinning process according to the invention.FIG. 14 is a cross-sectional view taken along the line XIV—XIV in FIG.13.

The carrier 1 in this embodiment has a plurality of suction pads 1 bprovided over one entire side of the base 1 a. Therefore, thesemiconductor wafer can be supported at a plurality of locations bythese suction pads 1 b.

Thus, even if some of the plurality of suction pads 1 b lose theirsuction forces by deterioration or deformation, it is assured that thesemiconductor wafer can be supported by the remaining pads 1 b.

FIG. 15 is a plan view of the carrier used in still another embodimentof the semiconductor wafer thinning process according to the invention.FIG. 16 is a cross-sectional view taken along the line XVI—XVI in FIG.15.

The carrier 1 in this embodiment has a smaller diameter than thesemiconductor wafer 2 so that the outer peripheral edge of thesemiconductor wafer 2 is projected from the carrier 1. In other words,the semiconductor wafer 2 of the wafer composite 10 overhangs thecarrier 1. In order that the supporting pins can hold the carrier 1without being in contact with the overhangs semiconductor wafer 2, pincontact projections 1 a ₁ slightly protruding outward from thesemiconductor wafer 2 are formed at three different locations facing thepins along the peripheral edge of the carrier. Such a structure as inthe overhangs semiconductor wafer 2 can be also applied to the carrier 1in other embodiments. In addition, it is of course possible that even inthe overhanging structure, the semiconductor wafer 2 may be directlysupported without the pin contact projections 1 a ₁ though it depends onthe final thickness of the semiconductor wafer 2.

In addition, the base 1 a has a hollow 6 which is communicated with avacuum hole 6 a connected to a vacuum pump 7, and a circular suctiongroove (adhesive member) 11 b for adhering to the semiconductor wafer 2by vacuum suction is concentrically formed in the surface of the base 1a so that the center of the groove is coincident with the center of thebase 1 a. The vacuum hole 6 a has a valve 8 mounted. This valve 8 isusually closed, but when a nozzle 7 a of the vacuum pump 7 is insertedinto the valve, the valve 8 is extended to open the vacuum hole 6 a. Thesuction groove 11 b is not always formed in a concentric circle on thebase 1 a, but may be of an arbitrary shape such as a spiral shape. Whilethe valve 8 is provided at the center of the base 1 a as illustrated inFIG. 16, it may be mounted on, for example, the outer peripheral side ofthe base 1 a. Moreover, the valve 8 may be of a complicated mechanicalstructure or of a simple elastic type such as rubber.

First, the nozzle 7 a is inserted into the vacuum hole 6 a to open thevalve 8 of the carrier 1, and the wafer 2 is attached onto the base 1 awhile the hollow 6 is evacuated by the vacuum pump 7. Then, after enoughevacuation is made until the semiconductor wafer 2 can be securely fixedto the base 1 a, the nozzle 7 a is withdrawn from the valve. Since thevalve 8 opens the vacuum hole 6 a to permit air to flow from the hollow6 to the outside while the nozzle 7 a stays inserted in the valve, butcloses the vacuum hole 6 a after the nozzle 7 a is withdrawn from thevalve, air can be prevented from flowing from the outside into thehollow 6 so that the semiconductor wafer 2 can be stuck onto the carrier1, thus forming the wafer composite 10.

After the wafer composite 10 is completed, the etchant L for thinning isspin-coated on the semiconductor wafer 2 of the wafer composite by theetching apparatus shown in FIG. 5 as described in the previousembodiment. Here, while the wafer composite 10 is being rotated, N₂ gas,for instance, is continuously blown from below against the wafercomposite. Since the semiconductor wafer 2 overhangs from the carrier 1as described above, the N₂ gas is blown against the downward outerperiphery of the main surface of the semiconductor wafer 2 without beingblocked by this carrier 1.

After the thinning process is finished, the wafer composite is attachedonto the dicing tape, and then the vacuum hole is opened so that thepressure in the hollow 6 can be restored to the atmospheric pressure.Accordingly, the suction force of the suction groove 11 b to thesemiconductor wafer 2 is lost, thus allowing the carrier 1 to be easilyseparated from the semiconductor wafer 2. Then, the semiconductor wafer2 on the dicing tape is diced into individual semiconductor chips.

According to the semiconductor wafer 2 processing technique of thisembodiment, since the wafer composite 10 is formed so that thesemiconductor wafer 2 overhangs the carrier and since the etchant L forthinning is spin-coated on the semiconductor wafer while air iscontinuously blown from below against the wafer composite 10, theetchant L can be prevented from flowing around the peripheral side intothe main surface, even though a large centrifugal force cannot beachieved because of spin-coating under a low revolution rate. Therefore,the circuit elements formed on the semiconductor wafer 2 can beprotected from being damaged by the etchant.

Moreover, since the semiconductor wafer 2 is stuck by vacuum suctiononto the carrier 1 to form the wafer composite 10, and since the reducedpressure in the hollow is restored to the atmospheric pressure afterthinning so that the wafer 2 and the carrier 1 can be separated, thecarrier 1 can be smoothly peeled off.

In addition, since the semiconductor wafer 2 is kept flat along the base1 a, the wafer 2 can be suppressed from warp.

It was previously described that the diameter of the wafer 2 may besmaller than or equal to that of the carrier 1 as is contrary to thisembodiment. In this case, if the outer periphery of the main surface ofthe semiconductor wafer 2 is tightly and securely fixed to the carrier 1without any gap, the etchant L can be prevented from flowing around theperipheral side into the main surface. Therefore, as in this embodiment,there is no need to spin-coat the etchant L while air is continuouslyblown against the wafer composite 10. Also, since the thin semiconductorwafer 2 does not overhang the carrier 1, it is easy to handle the wafercomposite 10. Moreover, since the entire main surface of thesemiconductor wafer 2 is covered by the carrier 1 so as to be shieldedfrom the external atmosphere, the rear surface of the semiconductorwafer 2 can be etched to be thinned by the dipping system in which thewafer composite 10 itself is dipped in the etchant L, not by thespinning type etcher.

FIG. 17 is a plan view of the carrier used in still another embodimentof the semiconductor thinning process according to the invention. FIG.18 is a cross-sectional view taken along the line XVIII—XVIII in FIG.17.

In this embodiment, suction holes 21 b are provided instead of thesuction groove 11 b given in the previous embodiment. In other words,the suction holes 21 b are formed in one surface of the base 1 a at aplurality of locations so as to be communicated with the vacuum hole 6 athrough which the hollow 6 is connected to the vacuum pump as in thesample of the suction groove 11 b. The semiconductor wafer 2 is suckedby the vacuum pump 7. Therefore, separation of the semiconductor wafer 2from the carrier 1 is made by restoration to atmospheric pressure.

The semiconductor wafer 2 may be combined with the carrier 1 to form thewafer composite 10 by the vacuum suction via a plurality of suctionholes 21 b thus formed.

FIG. 19 is a plan view of the carrier used in still another embodimentof the semiconductor wafer thinning process according to the invention.FIG. 20 is a cross-sectional view taken along the line XX—XX in FIG. 19.

In this embodiment, a porous member 31 b made of resin or metal isprovided on one side of the base 1 a instead of the suction groove 11 b.As illustrated in FIG. 19 at A, the porous member 31 b has a number ofsmall holes 31 b ₁ formed, which are communicated with the vacuum hole 6a through the hollow 6 as shown in FIG. 20. The semiconductor wafer 2 isstuck to the carrier 1 by the vacuum suction via the small holes 31 b ₁of the porous disk 31 b, and separated from the carrier by restorationto atmospheric pressure.

Thus, the semiconductor wafer 2 can also be combined with the carrier 1to form the wafer composite 10 by the vacuum suction via the porousmember 31 b.

FIG. 21 is a plan view of the carrier used in still another embodimentof the semiconductor wafer thinning process according to the invention.FIG. 22 is a cross-sectional diagram taken along the line XXII—XXII inFIG. 21. FIGS. 23 to 28 and FIG. 30 are flow diagrams of thesemiconductor wafer working process using the carrier shown in FIG. 21.FIGs. 29(a) and 29(b) diagrams useful for explaining the sucked stateand separated state between the semiconductor wafer and the carrier. Inthis embodiment, because the adhesion sheet 41 b ₁ illustrated in FIG.22 is transparent, a net (exfoliation) 41 b ₂ is seen through thisadhesion sheet 41 b ₁.

The adhesion member 41 b of the carrier 1 in this embodiment is formedof the net 41 b ₂ having a plurality of small recesses and its surfaceflush with that of the base 1 a, and the adhesion sheet 41 b ₁interposed between the net 41 b ₂ and the semiconductor wafer 2 (FIGS.23 to 30) so as to stick the wafer 2 to the base 1 a. The adhesion sheet41 b ₁ is made of a flexible, surface-smooth material such as a curableliquid polymer, namely, gelled silicone containing a curable component.Therefore, when a solid substance having a smooth surface such as thesemiconductor wafer 2 is placed on the adhesion sheet 41 b ₁, the entiresurfaces of the wafer 2 and adhesion sheet 41 b ₁ are made in intimatecontact with each other and fixed by interfacial facial adhesion. Inplace of the net 4lb₂, the base 1 a may have an irregular surface formedas an exfoliative portion.

A through-hole 1 a ₂ is formed in the base 1 a at its center, and isconnected to the vacuum pump when the semiconductor wafer 2 and thecarrier 1 are separated as described later.

The procedure of the semiconductor wafer 2 thinning process using thecarrier 1 will be described below. The procedure in this embodiment issubstantially the same as that in the previous embodiment mentionedfirst, and thus like elements will be described briefly.

First, as illustrated in FIG. 23, the semiconductor wafer 2 thinned to acertain thickness is pressed against the carrier 1. At this time, sincethe presence of looseness due to extension and slack in the adhesionsheet 41 b ₁ will cause the semiconductor 2 to vibrate when it isrotated, the adhesion sheet 41 b ₁ is required to be completely incontact with the surface of the base 1 a and net 41 b ₂. When a lightweight is loaded uniformly on the entire surface of the semiconductorwafer 2, an interfacial force is exerted between the semiconductor wafer2 and the adhesion sheet 41 b ₁, causing the semiconductor wafer 2 tostick to the carrier 1, so that the wafer composite 10 can be formed(FIG. 24). This wafer composite 10 is loaded in the etching apparatusshown in FIG. 5, and the etchant L is pin-coated on the rear surface ofthe semiconductor wafer 2 of the wafer composite 10 with thesemiconductor wafer side up (FIG. 25), thereby thinning it (FIG. 26).Then, after rinsing and drying, the wafer composite 10 is attached tothe dicing tape 4 (FIG. 27), and the through-hole 1 a ₂ of the base 1 ais connected to the vacuum pump 7 so that the semiconductor wafer issucked by vacuum (FIG. 28). Thus, the semiconductor wafer 2 and adhesionsheet 41 b ₁ securely fixed face to face as illustrated in FIG. 29 at(a) are shifted to, as it were, the point-contact state since theadhesion sheet 41 b ₁ is pulled into the small recesses of the net 41 bas shown in FIG. 29 at (b). After the interfacial force between both isextremely reduced by this shift, the carrier 1 is separated from thesemiconductor wafer 2. Thus, the thinned semiconductor wafer 2 remainsstuck to the dicing tape 4 (FIG. 30). Thereafter, the semiconductorwafer 2 is diced into individual semiconductor chips.

According to the semiconductor wafer 2 processing technique of thisembodiment, since the pressure in the surroundings of the net 41 b ₂ isreduced after thinning, thus causing the adhesion sheet 41 b ₁ to bepulled into the small recesses of the net 41 b ₂ so that thesemiconductor wafer 2 and the adhesion sheet 41 b ₁ are brought in tothe point-contact state under which the interfacial force is reduced toallow the carrier 1 to be separated from the semiconductor wafer 2, thecarrier 1 can be more easily peeled off from the semiconductor wafer 2,and thus the thin semiconductor wafer 2 can be mass-produced with highproductivity.

In addition, since the semiconductor wafer 2 can always be kept flatalong the base 1 a, it is possible to suppress the warp of thesemiconductor wafer 2.

FIGS. 31 to 37 are flow diagrams of the semiconductor wafer thinningprocess of still another embodiment according to the invention.

The carrier 1 depicted in FIG. 31 has a transparent sheet tape 52attached to the base 1 a with a transparent adhesive 53. On the surfaceof the sheet tape 52, is coated an adhesive of which the adhesion isreduced or lost by irradiating UV (ultraviolet) light 54 (FIG. 36), or aremovable UV cure-type adhesive (adhesive member) 51 b. Moreover, thebase 1 a is made of a transparent or semitransparent material throughwhich UV light 54 can penetrate, such as acrylic acid resin, or amaterial having transparency.

The procedure of the semiconductor wafer thinning process using thiscarrier 1 will be described below. The procedure of this embodiment issubstantially the same as that of the embodiment mentioned first, andthus like elements will be described briefly.

First, the semiconductor wafer 2 thinned to a certain thickness ispressed against the UV cure-type adhesive 51 b coated surface of thecarrier 1 as illustrated in FIG. 31. When a light weight is loadeduniformly on the entire surface of the semiconductor wafer 2, the UVcure-type adhesive 51 b is pressed by the semiconductor wafer 2, thusmaking the wafer 2 fixed to the carrier 1 to form the wafer composite 10(FIG. 32). Then, the wafer composite 10 is loaded in the etchingapparatus in such a manner that the rear surface of the semiconductorwafer 2 is placed up, and the semiconductor wafer is thinned by droppingthe etchant L on the rear surface of the wafer 2 while it is being spun(FIGS. 33 and 34). After rinsing and drying, the wafer composite 10 isattached to the dicing tape 4 (FIG. 35), and UV light 54 is irradiatedon the wafer composite 10 through the base 1 a (FIG. 36). The irradiatedUV light 54 penetrates the transparent base 1 a, sheet tape 52, andadhesive 53 and reaches the UV cure-type adhesive 51 b. Therefore,adhesion of the UV cure-type adhesive 51 b is reduced by the UV light54. At this time, the carrier 1 is pulled away from the semiconductorwafer 2, and thus the thinned semiconductor wafer 2 stays stuck to thedicing tape 4 (FIG. 37). Thereafter, the semiconductor wafer 2 is dicedinto individual semiconductor chips. In this case, the dicing tape 4 maybe made of a material of which the adhesion can be reduced by theirradiation of UV light. Thus, if UV light is irradiated on thesemiconductor wafer when the semiconductor chips after dicing are pickedup, the operation is easy.

According to the semiconductor wafer 2 processing technique of thisembodiment, the peeling-off operation can be performed with ease, sinceUV light 54, after thinning, is irradiated on the UV cure-type adhesive51 b used as an adhesive for bonding the semiconductor wafer 2 and thebase 1 a, thus reducing its adhesion so that the carrier 1 can be peeledoff from the semiconductor wafer 2.

In addition, since the adhesion between the carrier 1 and thesemiconductor wafer 2 is reduced by the irradiation of UV light 54,there is no heat effect on a member, such as the dicing tape 4, to whichthe semiconductor wafer 2 is transferred after thinning, and thus it ispossible to increase the freedom in the semiconductor production processdesign.

Moreover, since the thickness of the wafer composite 10 can be decreasedby use of UV cure-type adhesive 51 b, the wafer composite 10 can behandled like the normal-thickness semiconductor wafer without particularcare to the small thickness.

Also, since the semiconductor wafer 2 can always be kept flat along thebase 1 a, it is possible to suppress the warp of the semiconductor wafer2.

FIG. 38 is a plan view of the carrier used in the semiconductor waferthinning process of still another embodiment according to the invention.FIG. 39 is a cross-sectional view taken along the line XXXIX—XXXIX inFIG. 38.

The carrier 1 in this embodiment has the base 1 a made of a PET filmwith a thickness of, for example, 188 μm, and a temperature activationtype adhesive (adhesive member) 61 b, coated on the base 1 a, of whichthe adhesion is reduced or lost at a low temperature of 0° C. to 5° C.The base 1 a may be made of PET film of which the thickness is, forexample, 100 μm or 250 μm, or made of, for example, a plastic or glassplate other than PET film. The temperature activation type adhesive 61 bused is of the cool-off type in which the peel strength per 25-mm widthis 35 gf to 150 gf at a temperature of 10° C. to 90° C., and is reducedto 0 gf at a temperature of about 0° C. to 5° C. However, another typemay be used in which the temperature activation point is as high asabout 15° C. depending on the environment in which it is used. Thetemperature activation type adhesive 61 b in this specification is anadhesive of which the adhesion is reduced or lost by temperature change,and includes the cool-off type in which the adhesion is reduced at a lowtemperature as in this embodiment, and a warm-off type of which theadhesion is reduced at a high temperature.

In the semiconductor wafer thinning process using this carrier 1, first,the semiconductor wafer is attached onto the carrier 1 at normaltemperature to form the wafer composite, and the semiconductor wafer isthinned by the same etching process as in the previous embodiments.Then, the wafer composite is stuck on the dicing tape so that theadhesive surface adheres to the semiconductor wafer. Thereafter, thewafer composite on the tape is left in a low-temperature environmentsuch as a refrigerator for ten minutes so that the wafer composite iscooled to, for example, 3° C. Since the temperature activation typeadhesive 61 b is of the cool-off type in which the peel strength isreduced to about 0 gf at a temperature of 0° C. to 5° C. together withgreat reduction of the adhesion, the carrier 1 can be easily peeled offfrom the semiconductor wafer when the wafer composite is cooled to 3° C.

While the temperature activation type adhesive 61 b used in thisembodiment is of the cool-off type in which the adhesion is reduced at alow temperature, it may be of the warm-off type in which the adhesion isreduced at a high temperature within a temperature range in which thebase 1 a and the dicing tape are not affected by heat. In addition, ifthe dicing tape is made of a UV tape of which the adhesion is reduced bythe irradiation of UV light, the heat effect can be completelyeliminated.

According to the semiconductor wafer thinning technique of thisembodiment, the peeling-off operation can be easily performed since thecarrier 1 using the temperature activation type adhesive 61 b as abonding agent is peeled off from the semiconductor wafer when theadhesion is reduced by temperature change. In addition, since thecarrier 1 can be repeatedly used, the thinned semiconductor wafer can bemass-produced at low cost.

Moreover, since the wafer composite can be made thin by using PET filmfor the base 1 a, it can be handled like the normal-thicknesssemiconductor wafer. Also, since the cost can be reduced, the carrier 1is disposable.

Since the film-shaped base 1 a can be peeled off from the semiconductorwafer, the separation is easier than a plate-like and solid material. Inaddition, a protective tape for BG (back grinding) before etching forthinning can be used for the base 1 a.

Also, since the semiconductor wafer is always kept flat along the base 1a, the warp of the semiconductor wafer can be suppressed even by thecarrier 1 of this embodiment.

FIG. 40 is a cross-sectional diagram of the carrier used in thesemiconductor wafer thinning process of still another embodimentaccording to the invention.

The base 1 a of the carrier 1 according to this embodiment is made ofpressed-hard fibrous fluororesin in place of the PET film described inthe above embodiment. Thus, the bonding agent such as the temperatureactivation type adhesive 61 b can enter into the gaps of the fluororesinby an anchor effect so as to be surely coated on the base 1 a. Thebonding agent or adhesive member may be the UV cure-type adhesive 51 bmentioned in the above embodiments.

Thus, since the carrier 1 has its base 1 a made of fluororesin having afeature of resistance to acid, it is possible to use various bondingagents such as the temperature activation type adhesive 61 b that haslow adhesion to the base 1 a.

FIGS. 41 to 54 are flow diagrams of an embodiment of the IC cardproduction method according to the invention. FIG. 55 is an enlargedplan view of the electrode portion of a chip of the semiconductor wafershown in FIG. 41. FIG. 56 is a cross-sectional diagram taken along theline C₁ to C₁ in FIG. 55, FIG. 57 shows the details of FIG. 48, and FIG.58 is a plan view of the internal structure of the IC card producedaccording to this embodiment. FIG. 59 is a cross-sectional diagram takenalong the line C₂ to C₂ in FIG. 58, FIG. 60 is an enlargedcross-sectional view of portion A in FIG. 59, and FIG. 61 is an enlargedcross-sectional view of portion B in FIG. 60.

In the IC production method of this embodiment, first, the semiconductorwafer 2 having circuit elements built in the main surface, or in whichthe so-called wafer process is already completed, is prepared asillustrated in FIG. 41. Therefore, a passivation film 2 a (FIGS. 55 and56) made of, for example, Si₃N₄ film is formed on the main surface toshield the circuit elements from the external atmosphere so that thecharacteristics of the elements can be stabilized. In the illustratedexample, Au (gold) bumps 2 b are formed on the chip electrodes by, forexample, electrolytic plating or vacuum evaporation. Wiring conductors101 a (FIG. 58 and so on) on a card substrate 101 (FIG. 53 and others)which will be described later are electrically connected through the Aubumps 2 b to the chips. In this case, the chip electrodes may beconnected to the wiring conductors by wire bonding instead of the bumps.In addition, bumps made of other metal, such as Pb (phosphorus)/Sn (tin)bumps may be formed on the chip electrodes.

FIG. 55 shows the chip electrode of the semiconductor wafer 2. Asillustrated, the passivation film 2 a is deposited around the Au bump 2b on the chip. As shown in FIG. 56, or in the cross-sectional diagramtaken along the line C₁—C₁ in FIG. 55, the passivation film 2 aprotecting the element region A is formed of two layers: an inorganicpassivation film 2 a as an underlayer and an organic passivation film 2a ₂ as an upper layer. The inorganic passivation film 2 a ₁ is made of,for example, 1.2 μm-thick SiN (silicon nitride) and 0.6μm-thick SiO₂(silicon oxide), and the organic passivation film 2 a ₂ is made of, forexample, 2.3 μm-thick polyimide. On the element region A are formed, forexample, an Al electrode conductor 2 c of 0.8 μm-thickness, and anunderbump metal 2 d on the conductor 2 c. The Au bump 2 b of, forexample, 20 μm-height is formed on this underbump metal 2 d as a platedelectrode. In this embodiment, the underbump metal 2 d is made of Ti(titanium)/Pd (palladium) for increasing the adhesion and for metaldiffusion protection. It may be made of other metals, for example, TiW(titanium-tungsten), Cr (chromium) or Cu (copper).

Then, as shown in FIG. 42, a surface-protective resist 111 is coated onthe main surface of the semiconductor wafer 2, and heated. In addition,as shown in FIG. 43, a BG tape 112 for rear surface grinding is attachedon the main surface of the semiconductor wafer 2, and the rear side ofthe semiconductor wafer of, for example, 550 μm thickness is ground to athickness of, for example, 150 μm as shown in FIG. 44. Since the resist111 is coated on the main surface of the wafer, the surface of thesemiconductor wafer 2 can be protected from contamination by dust in theBG process.

After the semiconductor wafer 2 is thinned by the BG process, the BGtape 112 is peeled off as shown in FIG. 45, and then the resist 111 isremoved as shown in FIG. 46.

The carrier 1 is prepared which has a base made of, for example, 250μm-thick PET film and a normal adhesive (namely, not of the temperatureactivation type) coated on the base. Then, as shown in FIG. 47, thesemiconductor wafer 2 with its rear side up is attached onto the carrier1 to form the wafer composite 10. The carrier 1 may be of other typesused in the above embodiments.

Here, the thickness of the adhesive of the carrier 1 is equal to theheight of the Au bump 2 b, or 20 μm. Therefore, the adhesive acts notonly on the Au bump 2 b, but also on the passivation film 2 a on thewafer surface 20 μm lower than the Au bump 2 b. Thus, all the entirecarrier 1 is made in intimate contact with the semiconductor wafer 2 sothat both can be prevented from being peeled off from each other. Sincethe adhesive adheres to the wafer surface even though its thicknessexceeds the height of the Au bump 2 b, the thickness of the adhesive maybe larger than the height of the Au bump 2 b (namely, equal to or largerthan the height of the Au bump 2 b).

If the wafer composite 10 is formed, the etchant L is dropped on therear surface of the semiconductor wafer of the wafer composite with itswafer side up, thinning it by spin etching to a thickness of, forexample, 50 μm. Here, if the carrier were not attached to thesemiconductor wafer, the semiconductor wafer would be warped whenthinned to such a level because the rigidity of the semiconductor wafer2 is reduced so that the residual stress in the passivation film 2 a isreleased. Particularly when the compressing stress in SiN of inorganicpassivation film 2 a ₁ and the tension stress involved with the curingcontraction of polyimide of organic passivation film 2 a ₂ are released,the surface of the semiconductor wafer 2 would be, creatingirregularities. Thus, If the semiconductor wafer 2 is stuck to thecarrier 1 to form the wafer composite 10 as in this embodiment, the baseconstituting the carrier 1 reinforces the semiconductor wafer 2 tocompensate for the reduction of rigidity, and suppresses the release ofthe stress in the passivation film 2 a, with the result that the thinnedsemiconductor wafer 2 is never warped. In this embodiment, asillustrated in FIG. 48, the diameter of the semiconductor wafer 2 islarger than that of the carrier 1 so that the semiconductor wafer 2overhangs the carrier 1. Thus, in order that the etchant L can beprevented from flowing around onto the main surface upon etching, N₂ gas(nitrogen gas) G, for instance, is blown against the lower side of thewafer composite 10.

For spin etching, an etcher 113 of, for example, pinless chuck type isused as illustrated in FIG. 57. Here, suction grooves 113 a, to beevacuated are formed in the surface of a working stage 113 a at aplurality of locations. The suction grooves 113 a ₁ are communicatedwith an evacuation groove 113 b ₁ of an evacuation tube 113 b connectedto a vacuum pump. Since the suction grooves 113 a, are evacuated throughthe evacuation groove 113 b ₁, the semiconductor wafer 2 is sucked andfixed to the working stage 113 a. Therefore, although the semiconductorwafer 2 overhangs the working stage 113 a, it is not necessary tosupport its periphery by supporting pins. Thus, the etchant L can beproperly dropped on the right place without staying at unnecessarylocations of supporting pins, such that defects and dents can beprevented from locally occurring on the semiconductor wafer duringetching.

Since the flowing-around problem of the etchant L mentioned above can besolved by strongly combining the semiconductor wafer 2 and the carrier 1to be in intimate contact with each other, the diameter of thesemiconductor wafer 2 may be made smaller than that of the carrier 1. Inthat case, the N₂ gas G need not be blown against the wafer composite10, and also other etching system such as a dipping system as describedabove can be employed for thinning the semiconductor wafer 2.

After the semiconductor wafer 2 is thinned to a thickness of about 50μm, the wafer composite 10 is attached to the dicing tape 4 with itssemiconductor wafer 2 side up as shown in FIG. 49. Then, as illustratedin FIG. 50, the lower surface of the tape is fixed to a vacuum suctiontable 114, and the carrier 1 is peeled off from the semiconductor wafer2 by peeling.

Thereafter, as shown in FIG. 51, the semiconductor wafer 2 is dividedinto individual semiconductor chips P by, for example, full cutting. Asshown in FIG. 52, UV light 54 is then irradiated on the UV adhesive ofthe dicing tape 4, thus reducing or loosing or losing the adhesionbetween the dicing tape 4 and the semiconductor wafer 2.

As illustrated in FIG. 53, the card substrate 101 is set above thesemiconductor chip P, and the semiconductor chip P is tentativelyattached by a direct transfer system onto the card substrate 101 at achip mounting location with the anisotropically conductive adhesive 116being interposed therebetween. In the direct transfer system, the cardsubstrate is stuck up from below by a sticking-up pin 114. Then, asshown in FIG. 54, the chip P is fully bonded to the card substrate by abonding tool 118 with the lower side being supported by a pedestal 117.In this bonding process, the semiconductor chip is heated and pressedagainst the card substrate.

FIG. 58 illustrates an IC card 100 formed by the card substrate 101 withthe semiconductor chips P thus mounted. The IC card 100 is a wirelesstype IC card assembled by a laminate system. The IC card has its cardsubstrate 101 surrounded by a printed coil 101 b which is formed in aring shape along the periphery of the IC substrate and which serves asan antenna for receiving an external signal and transmitting an internalsignal. The IC card has also a wiring conductor 110 a formed extendingfrom the printed coil 101 b. The wiring conductor 101 a connects theprinted coil 101 b and the semiconductor chips P, so that signals aretransmitted and received by the semiconductor chips P having variousfunctions.

The members of the IC card 100 are laminated with an adhesive as shownin FIG. 59. In other words, a pacer 102 with recesses provided forreceiving the printed coil 101 b, wiring conductor 101 a. and mountedsemiconductor chips P is bonded face to face to the chip-mounded side ofthe card substrate 101, so that the spacer 102 is flush with thesemiconductor chips P. In addition, a thickness correcting sheet 103 isattached to the spacer 102 so as to adjust the thickness to bring thesemiconductor chips P such as IC chips and capacitor chips to thebending neutral point of the IC card 100 (the bending neutral point isthe center of the thickness of the IC card 100 if the members of bothsides of the semiconductor chip P are all equal). When the IC card 100is bent, the compressing force and tension exerted on the semiconductorchips P can be relieved by this thickness correcting sheet. Moreover,decorated exterior plates 104 a, 104 b that serve as the front and rearsurfaces of the IC card 100 are respectively bonded on both sides of thelaminate of card substrate 101, spacer 102 and thickness correctingsheet 103. In this embodiment, the card substrate 101, thicknesscorrecting sheet 103 and decorated exterior plates 104 a, 104 b are madeof PFT.

FIG. 60 is an enlarged view of portion A of FIG. 59. In the chip-mountedregion of the IC card 100, the Au bumps 2 b are electrically connectedto the wiring conductor 101 a. through the anisotropically conductiveadhesive 116 and by its adhesion so that the semiconductors P aremounted on the card substrate 101. Also, the thickness correcting sheet103 is bonded to the card substrate 101 with the spacer 102 interposedtherebetween. FIG. 61 is an enlarged view of portion B of FIG. 60. Theanisotropically conductive adhesive 116 is formed by an adhesive 116 band conductive particles 116 a each of which is formed of, for example,a plastic ball of about 5 μm-diameter with an Au coating. Part of eachof the conductive particles 116 a of the anisotropically conductiveadhesive 116 are pressed between the Au bump 2 b and the wiringconductor 101 a. Thus, the Au bump 2 b and the wiring conductor 101 acan be electrically connected through the crushed conductive particles116 a.

According to the IC card 100 production method of this embodiment, sincethe carrier 1 and the semiconductor wafer 2 are combined into the wafercomposite 10 of which the semiconductor wafer 2 is then thinned to athickness of, for example, 50 μm without any crack or warp, and dicedinto semiconductor chips P which are used in the assembly process forthe IC card 100, the IC card 100 can be made thinner.

The present invention is not limited by the specific embodimentspreviously mentioned in detail, but is capable of various changes andmodifications without departing from the scope of the invention.

For example, the base 1 a may be molded out of fluororesin, glass plateor epoxy resin, and the suction pad 1 b may be a liquid such as water.In this case, the interfacial force is exerted between the semiconductorwafer 2 and the base 1 a so that both materials can be bonded together,and in order to peel the carrier 1 from the semiconductor wafer 2,ultrasonic wave is applied to the wafer composite.

INDUSTRIAL APPLICABILITY

The semiconductor wafer processing technique of the invention is usefulfor the application to the semiconductor chips incorporated inultra-thin type electronic devices such as IC cards.

What is claimed is:
 1. A semiconductor wafer processing method,comprising the steps of: providing a semiconductor wafer having a mainsurface and a rear surface which is opposite to said main surface, saidsemiconductor wafer having circuit elements formed in said main surface;providing a plate-like carrier formed of a base and an adhesive memberprovided on one surface of said base, said carrier having a diameterwhich is smaller than that of said semiconductor wafer; adhering saidsemiconductor wafer to said carrier in such a manner that said mainsurface of said wafer contacts with said adhesive member, a rear surfaceof said wafer with no circuit elements formed therein is opposite tosaid carrier, and the entire periphery of said semiconductor waferoverhangs said carrier, to form a wafer composite; while holding saidwafer composite with said semiconductor wafer up, spin-coating anetchant on the rear surface of said semiconductor wafer whilecontinuously blowing gas from below against said wafer composite,thereby thinning said semiconductor wafer; adhering to a dicing sheetthe thinned rear surface of said semiconductor wafer of said wafercomposite after said thinning step, and peeling off said carrier fromsaid wafer composite; and dicing said semiconductor wafer on said dicingsheet into individual semiconductor chips; wherein said step ofproviding a plate-like carrier provides said adhesive member as a liquidthat acts as an adhesive in such a manner that during said step ofadhering said semiconductor wafer to said carrier, said semiconductorwafer and said base are in intimate contact with each other by theinterfacial force exerted therebetween, and that during said step ofpeeling off said carrier from said wafer composite, the semiconductorwafer is peeled off from the base by ultrasonic waves.
 2. Asemiconductor wafer processing method, comprising the steps of:providing a semiconductor wafer having a main surface and a rear surfacewhich is opposite to said main surface, said semiconductor wafer havingcircuit elements and bonding pads formed in said main surface and havingbump electrodes at said bonding pads; providing a film-like carrierformed of a base, a sheet tape on one surface of said base and anadhesive member provided on said sheet tape; adhering said semiconductorwafer to said carrier in such a manner that said main surface of saidwafer contacts with said adhesive member, said bump electrodes areburied in said adhesive member, and a rear surface of said wafer with nocircuit elements formed therein is opposite to said carrier to form awafer composite; holding said wafer composite with said semiconductorwafer up; reducing a thickness of the semiconductor wafer by grindingthe rear surface of the semiconductor wafer, thereby providing a firstthickness and a first rear surface opposite to the main surface; andreducing said first thickness by contacting an etching solution with thefirst rear surface, thereby providing a second thickness and a secondrear surface.
 3. A semiconductor wafer processing method according toclaim 2, wherein said sheet tape is a flexible layer that is moreflexible than said base.
 4. A semiconductor wafer processing methodaccording to claim 2, wherein said adhesive member has a thickness whichis equal to or larger than a height of said bump electrodes in athickness direction of said semiconductor wafer.